Seasonal restrictions failing

by Cat Urbigkit

The 2005 annual report for the ongoing Sublette Mule Deer Study was recently completed and released by Western EcoSystems Technology Incorporated. The study is a collaborative effort between industry and agencies to monitor impacts of natural gas development activity on the deer population.

The study examines four characteristics of the deer population, including recruitment, adult doe survival, over-winter fawn survival and abundance. The study used a "treatment" area consisting of the area of the Mesa experiencing gas development, and a "control" area of the Pinedale Front where development isn't expected to occur.

The 2005 report found that recruitment (i.e., doe/fawn ratios) in the treatment and control areas was essentially the same since development began. Estimates of over-winter adult survival were lower in the development area for three of the five years since development began, and over-winter fawn survival was lower four of five years. The only year over-winter fawn survival was not lower in the development area was in the harsh winter of 2003-04, when high fawn mortality would be expected in both treatment and control areas.

"While these individual point estimates of over-winter adult and fawn survival were not statistically different between treatment and control areas, the long-term trends suggest deer in the treatment may not be performing as well as deer in the control," the report noted.

In addition, deep numbers dropped on the Mesa during the study.

"Of particular concern is the decreasing abundance estimates in the treatment area, dropping from 5,228 in 2002 to 2,818 in 2005," the report said. "This four-year, 46-percent reduction in deer abundance is disconcerting because there is no concurrent evidence of a population decline in the control area. At this point in time we cannot detect any positive or negative trends in the control area, but abundance in the treatment area has significantly declined since 2002."

The report continued: "Following the severe winter and associated high mortality rates in 2003-04, we expected deer abundance to increase the following year in both treatment and control areas, given the exceptionally mild 2004-05 winter. While an increase was evident in the control area, abundance continued to decline in the treatment area."

The WEST researchers stated that population changes on the Mesa were the result of reduced over-winter fawn survival, lower adult survival and migration. The first GPS-collared deer to emigrate from the Mesa and occupy a new, distinct winter range was documented during the 2003-04 winter, according to the report.

Deer No. 862, captured on the Mesa in December 2003, moved around the Mesa for three weeks, then left the area and migrated 20-25 miles southwest. This deer spent the remaining winter months in a different winter range characterized by sagebrush draws located near the Calpet Road south of Big Piney. In the spring of 2004 this deer used the same migration route to move back through the western edge of the Mesa, through the Trapper's Point Bottleneck, and onto summer ranges. The deer returned in the fall of 2004 through Trapper's Point, but did not move into the central portion of the Mesa, rather it moved quickly down the western edge and returned to the Big Piney winter range via the migration route it used the year before. This was the first GPS-collared deer to have left the Mesa and moved on to a different winter range, the report noted.

The objective of the deer study was to evaluate potential impacts of natural gas development on mule deer in terms of direct habitat loss, changes in habitat selection and population performance.

Direct habitat losses: Through August 2004, approximately 1,029 acres of the Mesa had been disturbed, of which 79 percent was due to wellpad construction and 21 percent to access roads. Each year development has progressed, well pads account for relatively more direct habitat loss than access roads.

Habitat selection patterns: During years one through three of gas development, habitat selection models and predictive maps suggested mule deer were less likely to occupy habitats in close proximity to well pads than those farther away. Changes in habitat selection appeared to be immediate and no evidence of well pad acclimation occurred through the first three years of development, rather deer selected areas farther from well pads as development progressed. The lower levels of deer use near well pads suggested indirect habitat losses may be substantially larger than direct habitat losses.

Additionally, some areas classified as high deer use prior to development changed to areas of low use following development. If areas classified as high use before development were those preferred by deer, then observed shifts in their distribution were towards less preferred and presumably less suitable habitats.

Population performance: The combination of changes in births, deaths and emigration resulted in an estimated 46-percent reduction in deer abundance over four years.

Management implications

The report suggested that using seasonal restrictions to protect mule deer aren't working as intended. The report noted, "Major shifts in the distribution of mule deer on the Mesa occurred during years one through three of development even though drilling on federal lands was largely restricted to non-winter months."

The report concluded: "In deep-gas fields like the PAPA where well densities range from four to 16 pads per section, the number of producing well pads and associated human activity may negate the potential effectiveness of timing restrictions on drilling activities as a means to reduce disturbance to wintering deer. Reducing disturbance to wintering mule deer may require restrictions or approaches that minimize the level of human activity during both production and development phases of wells."

In a boost to the natural gas operators seeking to eliminate seasonal restrictions in favor of a more comprehensive multiple directional well development program operating year-round, the report stated: "Directional drilling technology offers promising new methods for reducing surface disturbance and human activity. Limiting public access and road management strategies may also be a necessary part of mitigation plans."